Influence of the Fukushima Dai-ichi Nuclear Power Plant accident on environmental radioactivity in Aomori Prefecture

Radioactive nuclides with a short half-life, such as ¹³¹I and ¹³⁴Cs, were detected in environmental samples collected in Aomori Prefecture after the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. In addition, the observed ¹³⁷Cs concentration was increased over the background level. The gaseous ¹³¹I concentration in air observed in April was higher than that observed in March immediately after the accident. Using a backward trajectory analysis, the authors found that the air mass had passed the vicinity of the Fukushima Dai-ichi Nuclear Power Plant when the gaseous ¹³¹I concentration in air was increasing. Maximum ¹³¹I and radioactive Cs concentrations in daily fallout samples collected in Aomori city were observed on 28 April, when ¹³¹I was also detected in air. ¹³⁴Cs and ¹³⁷Cs concentration ratios in pine needles and pasture grass were nearly equal to 1, which indicates that the source of these radionuclides was the nuclear power plant accident. (authors)